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STRLEN

Introduction​

In Dragonfly, as well as in Redis and Valkey, the STRLEN command is used to get the number of bytes in a string value stored at a given key. This command is useful when you want to measure the length of a string, for example when validating input length or when you need to allocate storage based on string size.

Syntax​

STRLEN key
  • Time complexity: O(1)
  • ACL categories: @read, @string, @fast

Parameter Explanations​

  • key: The key of the string for which the length is calculated.

Return Values​

The command returns an integer representing the length of the string, in bytes.

Code Examples​

Basic Example​

Get the length of a string:

dragonfly> SET mykey "Dragonfly"
OK
dragonfly> STRLEN mykey
(integer) 9

Length of an Empty String​

If the string is an empty string, return 0:

dragonfly> SET mykey ""
OK
dragonfly> STRLEN mykey
(integer) 0

STRLEN on Non-Existent Keys​

When the key does not exist, STRLEN will return 0:

dragonfly> STRLEN non_existent_key
(integer) 0

Using STRLEN with Multibyte Characters​

Bear in mind that STRLEN returns the length in bytes, not characters. For example, a string with multibyte characters will have a byte length that may differ from its character count:

dragonfly> SET mykey "你好"
OK
dragonfly> STRLEN mykey
(integer) 6  # Most Chinese characters require 3 bytes each in UTF-8 encoding.

Best Practices​

  • Use STRLEN to check the byte size of string values before performing operations that might depend on their length.
  • Be aware that for multibyte character encodings (like UTF-8), the byte size might not be equivalent to the number of characters in the string.

Common Mistakes​

  • Confusing string length in characters with string length in bytes. Remember, STRLEN returns the byte length, which may vary for strings containing multibyte characters.
  • Assuming STRLEN will throw an error for non-existent keys. In fact, it simply returns 0 in such cases.

FAQs​

What happens if the string contains multibyte characters?​

STRLEN measures the string length in bytes, not in characters. So if your string contains multibyte characters, such as emojis or characters from non-Latin alphabets like Chinese, the byte size will be higher than the number of characters.

What if the key stores a non-string data type?​

If the value stored at the key is not a string (e.g., a list, set, or hash), STRLEN will return an error. You should ensure the key holds a string value before using this command.